Technical Field
Embodiments of the present invention generally relate to an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having at least two of copying, printing, facsimile transmission, plotting, and scanning capabilities, and an image formation method.
Description of the Related Art
There are image forming apparatuses that cyclically change charging power of a charger to charge a latent image bearer while cyclically changing a developing bias applied to a developer bearer of a developing device during an image forming operation of an image forming device.
For example, there are image forming apparatuses that form a latent image on the latent image bearer and develop the latent image, thereby forming a toner image, while cyclically changing the charging power and the developing bias. Specifically, the developing device develops an electrostatic latent image on a photoconductor, serving as the latent image bearer, with developer borne on a developing roller (i.e., a developer bearer), to obtain a toner image. At that time, due to distortion of external shape of the photoconductor or the like, the gap (i.e., a developing gap) between the photoconductor and the developing roller may fluctuate cyclically in accordance with rotation of the photoconductor. Such fluctuations result in cyclic density fluctuation of solid image portions of the image. Typically, image forming apparatuses perform a control operation to suppress such fluctuation. For example, the developing bias is cyclically changed based on readings by a rotary encoder detecting the rotation attitude of the photoconductor and predetermined development change pattern data. Cyclically changing the developing bias can suppress the cyclic density fluctuation of solid image portions resulting from fluctuations in the development gap. Additionally, the charging bias, which is applied to the charger to uniformly charge the photoconductor, is changed cyclically. Specifically, the charging bias is cyclically changed based on the results of detection of rotation attitude of the photoconductor and predetermined charging change pattern data. This operation is to suppress cyclic density fluctuation of halftone image portions caused by cyclically changing the developing bias. Thus, the cyclic density fluctuation of solid image portions and the cyclic density fluctuation of halftone image portions are supposedly suppressed.